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Measuring VIDEO signals with a oscilloscope?

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walters

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When measuring RED,GREEN,BLUE video analog signals with a oscilloscope
all i see is noise and fuzzy waveforms under 1 volt is this right?

When measure RED,GREEN,BLUE video analog signals with a oscilloscope what am i actually seeing? this isn't a true measurement right cause its a oscilloscope and not a video waveform monitor

But i read that when troubleshooting video gear or TV's you CAN NOT use a oscilloscope because the RED,GREEN,BLUE signals are to high of frequency is this true?

The RED,GREEN ,BLUe video signals are under 1 volt is this true?
 

walters

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Are video signals AC voltages or something different than AC voltages and DC voltages? the video signals don't look like AC voltages or DC voltages to me they look different what kind of AC voltages are they please?
 

kevpat

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The video signal you are looking at will most likely be amplitude modulated and yes it should be no more than 1V Pk-PK and you can certainly view the waveform on an oscilloscope. To understand what you are seeing on your scope I would recommend having a look at a Tektronix tutorial on measuring video on their website. It will certainly explain things clearer than I can here.
 

walters

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Can you please explain some video signal using the oscilloscope? how to measure

I still don't know what RED video voltage should be?

what the GREEN video voltage should be?

What the Blue video voltage should be?
 

mister_rf

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The Waveform monitor is an oscilloscope that has been custom configured for television monitoring. It is used to measure the voltage of the signal and to check that all the pulses and scans of the signal are occurring at the proper times.

Color information in video is derived from linear (tristimulus) red, green and blue (RGB) components. Due to CRT display technology limitations, these fundamental colors need to be manipulated in a non-linear form known as gamma-corrected colors. Normally a notation R'G'B' will be used for. In TV makes its luma Y' signal by summing weighted gamma-corrected signals
So we refer to luminance as Y'
Y’ = 0.299R' + 0.587G' + 0.114B'

First of all the measurements are relative to the place where the signals are used.
At the inputs if we compare to a standard video composite level of 1Vpp, Y' is maximum 714mV for NTSC and 700mV for PAL video signal so al R'G'B' signal are the same maximum 0.714/0.7Vpp, and more important those values depends on the video signal applied.



Read more here
https://www.poynton.com/notes/colour_and_gamma/ColorFAQ.html
https://en.wikipedia.org/wiki/Gamma_correction
A simplified RGB signal flow chart
**broken link removed**
 

TAMAWOOD

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Use DC and TVsync as a starting point. Video signals are very difficult to see on anything under 20MHz Analogue. I have a TV line selector which allows me to each line and it is extremely difficult to see with an analogue scope. Don't be afraid to turn the brightness up.
 

walters

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How do i set up my oscilloscope to measure RGB signals? VGA signals? composite signals please?

a standard video composite level of 1Vpp, Y' is maximum 714mV for NTSC and 700mV for PAL video signal so al R'G'B' signal are the same maximum 0.714/0.7Vpp, and more important those values depends on the video signal applied.

So on my oscilloscope my white will read ""714mV"" Peak to peak? is it a squarewaveform type looking wave? i think i see the sync pulse with it too is this correct?

When measuring RGB signals , on the oscilloscope they will read .7volts peak to peak? will it look like a squarewaveform type? will the sync pulse be superimposed with it too?

VGA is composite RGB right?

When measure VGA signals the red video signal will be .7volts p/p also? the green video signal will be .7volts p./p ? and the blue wil be .7volts p/p?

VGA video signals on the oscilloscope look like squarewaveform with different duty cycles? or what do they look like?

RGB video signals on the oscilloscope look like squarewaveforms with different duty cycles? or what do they look ilke ?

composite video signals on the oscilloscope look like squarewaveforms with different duty cycles? or what do they look like?

Added after 49 minutes:

Video signals are DC , why are video signals DC?

Composite video signal chart:

Green is 330mV or 61.8 IRE ?
Red is 280mV or 35.2 IRE?
Blue is 50 mV or 18.0 IRE?

White is 714mV or 100 IRE

Black is 5mV or 7.5 IRE?

Are these RGB and Black the right millivolts ?
 

walters

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can anyone help out about this please
 

echo47

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For composite signals, try this info:

"NTSC Video Measurements"
https://www.tek.com/Measurement/App_Notes/NTSC_Video_Msmt/

"NTSC Systems Television Measurements"
https://www.tek.com/Measurement/App_Notes/25_7049/eng/

"PAL Systems, Television Measurements"
https://www.tek.com/Measurement/App_Notes/25_7075/eng/25W_7075_3.pdf

Monochrome waveforms usually look like composite waveforms without the chroma component.

RGB waveforms usually look like monochrome waveforms, except there are three of them, of course. Also, the sync component may be omitted from the red and blue waveforms (aka "sync on green").

VGA waveforms usually look like RGB waveforms, except the sync component is moved to separate H and V pins. Also, VGA's horizontal and vertical rates are typically faster than television signals.
 

walters

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echo how should i set up my oscilloscope for displaying RBG and component video please?

and Why is video RBG and component video DC voltages and not AC? i dont' get it ??
 

echo47

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In general, set your oscilloscope to trigger on the sync pulses at the bottom of the composite waveform, or at the bottom of the RGB video's green waveform, or at the bottom of the component video's Y signal, or on one of VGA's sync signals. Then use your scope's other channels to view the other signals. Triggering on the analog sync tip may be difficult if your scope doesn't have a TV Trigger button.

RGB video and component video signals are not simply DC voltages. All the signals carry interesting waveforms.
 

walters

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The red,green,blue video signals each have different dutycycle on/off times to produce different FREQUENCYs at DC voltages right?

it seems that the RED signal has a dutycycle on/off timing to have a frequency at Xhz, at a DC voltage is this right?

The blue video signal has a dutycycle on/off time to have a frequency at Xhz at a DC voltage is this right?

The green video signal has a dutycycle on/off time to have frequency of Xhz at a DC voltage is this right?

Added after 2 minutes:

RGB video and component video signals are not simply DC voltages. All the signals carry interesting waveforms


Then if they aren't DC voltages what are they please explain more ? cause its seem like RGB video and component video signals are OTHER than DC and AC voltage but i don't know what to call them or relate them too

Added after 7 minutes:

""In general, set your oscilloscope to trigger on the sync pulses at the bottom of the composite waveform, or at the bottom of the RGB video's green waveform, or at the bottom of the component video's Y signal, or on one of VGA's sync signals. Then use your scope's other channels to view the other signals. Triggering on the analog sync tip may be difficult if your scope doesn't have a TV Trigger button""


Wait i don't understand or make it more clear please

I set my oscilloscope on TV triggering when measuring composite,RGB,VGA right?

1.) The problem i don't get is how do you SEPERATE the sync pulses,verical and horizonal pulses to go to "channel#1 on the oscilloscope"?

2.) Because composite mixes the sync,verical and horizontal signals into the Red,green,blue signals you can not seperate them, so how can i seperate them then?

3.) I would have to put my oscilloscope on DUAL MODE too , to see 2 channels at once right?

4.) Once i have seperated the sync,hortizonal,vertical on channel#1 how can i make the oscilloscope trigger the BOTTOM of the pulse and not the "top"?

Added after 1 hours:

How do you set the oscilloscope for for negative-going trigger?

I still don't know how to seperate the triggering on channel#1 and the composite or RGB on channel#2

example

RGB has 3 wires ,

i put the "Green wire" on channel#1 on the oscilloscope and set the oscilloscope to negative-going triggering right? but how?

Then i put the "Green wire" on channel#2 to see the color information or green channel voltage and set it to TV triggering?
 

FvM

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The questions basically suggest that you haven't get a clue how analog television works. Otherwise you wouldn't ask, why signals have "different duty cycle", or if they are AC or DC. I think, it's usesless to analyze RGB signals without a basic understanding of their meaning.

With an oscilloscope, I suggest to watch a test picture with a large color bar, that's what's generally used for service purposes when testing RGB channel signal transmission. The RGB signals have a simple structure here and you hopefully can get an intuitive understanding how they work.
 

mister_rf

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In general RGB signals can be categorized as having both AC (time varying) and DC (constant) components although one of these may be zero. That's why you need to set the oscilloscope on DC.

VGA is a high-resolution video standard used mostly for computer monitors, where ability to transmit a sharp, detailed image is essential. VGA uses separate wires to transmit the three color component signals and vertical and horizontal synchronization signals.
On RGB you may have a separate SYNC signal or a combined sync in the Green channel, named usually sync-on-green.
To visualize some signal you need to have a good synchronization.

If you use a two channel oscilloscope to obtain a proper synchronization you need to keep one channel blocked for the sync signals and with the second one to measure the need signals: R, G, B.
In the case of the combined signal =sync + Green info, you will keep the green channel for the synchronization.

See some pictures for better understanding.
I want to specify: the pictures aren’t accurate, it’s only to translate in ''graphics'' some ideas. :D
 

walters

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Thanks alot for the pictures do you have any more like this to show the voltages of the RGB and composite signals too please?

"If you use a two channel oscilloscope to obtain a proper synchronization you need to keep one channel blocked for the sync signals and with the second one to measure the need signals: R, G, B."

How do i set up a 2 channel oscilloscope to have channel#1 be the sync channel?

RGB has 3 wires , composite has 1 wire do i just parrallel the wires ?

Can you please give me a "block diagram" how to hook up RGB wires up to a oscilloscope to have channel#1 be the sync channel and channel#2 to be the color analog RGB channel please? and for composite too a block diagram?
 

mister_rf

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First read this about how to use an oscilloscope

https://www.williamson-labs.com/scope-main.htm
https://www.tek.com/Measurement/App_Notes/XYZs/03W_8605_2.pdf
https://www.facstaff.bucknell.edu/mastascu/eLabs/Scope/Scope1.html
https://www.doctronics.co.uk/scope.htm
https://www.practicalphysics.org/go...opic_id=$parameters.topic_id&collection_id=93
https://www.best-microcontroller-projects.com/how-to-use-an-oscilloscope.html
https://web.telia.com/~u85920178/scope/osc-0.htm
There's no special diagrams in order to do the measurements on two channels oscilloscope..
You need to discover how to trigger in a multi-channel scopes, you need to choose one channel to trigger, and other channels to be displayed. The basic idea is how to use it if the signals don’t have a sync on it and will be more difficult to synchronize the scope, so here’s the situation to choose one channel with sync, usually green channel, and to use the second one to view the remaining signals.

In a composite signal you have all the data inside so you need usually only one channel. On the same cannel you can do all measurements and have the trigger fixed on that signal.
 

walters

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mister_rf

Can you tell me anything else u know about video signal analysis? or video signal waveform analysis please?

Or just about troubleshooting and testing video signal waveforms and circuits that you know please?
 

walters

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I have these video colour corrector boxes and VGA to RGB converts boxes

On the oscilloscope what is displayed is ENCODED and modulated signals only of the video , its like really fast dots, and squares , looks very hazey also , but when you turn the times per division knob the encoded/modulated video waveforms turns into little squares,dots,lines
 

echo47

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Squares, dots, and lines? Are you sure your oscilloscope is working properly? Try using a good old-fashioned analog oscilloscope. Some digital scopes are terrible for viewing waveforms like this.

Here's an NTSC composite video signal (from a camcorder) as displayed on my Tektronix TDS 3054B scope. If I had an RGB signal to show you, each of the three signals would probably look similar to this, except without the color bursts, and possibly without the sync pulses (they may be on a different wire).
 

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